I. Field of the Invention
The present invention relates to a system and methods generally aimed at surgery. More particularly, the present invention is directed at a system and related methods for performing dynamic pedicle integrity assessments involving the use of neurophysiology.
II. Description of Related Art
A trend in spinal surgery is toward performing surgery in a minimally invasive or minimal access fashion to avoid the trauma of so-called open or “direct access” procedures. A specific area of interest is in the placement of pedicle screws (percutaneous and open), which are typically employed to effect posterior fixation in spinal fusion procedures. While great strides are being made in this area, a risk exists that the pedicle may become breached, cracked, or otherwise compromised due to the formation and/or preparation of the pilot hole (designed to receive a pedicle screw) and/or due to the introduction of the pedicle screw into the pilot hole. If the pedicle (or more specifically, the cortex of the medial wall, lateral wall, superior wall and/or inferior wall) is breached, cracked, or otherwise compromised, the patient may experience pain or neurologic deficit due to unwanted contact between the pedicle screw and exiting nerve roots. This oftentimes necessitates revision surgery, which is disadvantageously painful for the patient and costly, both in terms of recovery time and hospitalization.
Various attempts have been undertaken at performing pedicle integrity assessments. As used herein, the term “pedicle integrity assessment” is defined as detecting or otherwise determining whether a part of a pedicle has been breached, cracked, or otherwise compromised due to the formation and/or preparation of the pilot hole (designed to receive a pedicle screw) and/or due to the introduction of the pedicle screw into the pilot hole. “Formation” is defined as the act of creating an initial pilot hole in a pedicle, such as through the use of a drill or other hole-forming element. “Preparation” is defined as the act of refining or otherwise acting upon the interior of the pilot hole to further prepare it to receive a pedicle screw, such as by introducing a tap or reamer element into the initial pilot hole. “Introduction” is defined as the act of inserting or otherwise placing a pedicle screw into the initially formed and/or prepared pilot hole, such as by screwing the pedicle screw into the pilot hole via a screw driver or similar element.
Among the attempts, X-ray and other imaging systems have been employed, but these are typically quite expensive and are oftentimes limited in terms of resolution such that pedicle breaches may fail to be detected.
Still other attempts involve capitalizing on the insulating characteristics of bone (specifically, that of the walls of the pedicle) and the conductivity of the exiting nerve roots themselves. That is, if a wall of the pedicle is breached, a stimulation signal applied to the pedicle screw and/or the pilot hole (prior to screw introduction) will cause the various muscle groups coupled to the exiting nerve roots to contract. If the pedicle wall has not been breached, the insulating nature of the pedicle will prevent the stimulation signal from innervating the given nerve roots such that the associated muscle groups will not twitch. Traditional EMG monitoring systems may be employed to augment the ability to detect such innervation. A drawback with such prior art systems is that they do not lend themselves to assessing pedicle integrity in a dynamic fashion (that is, during the formation, preparation and/or introduction stages of pedicle screw fixation, whether in open or percutaneous procedures). A similar drawback exists, particularly in open cases, where fluids (e.g. blood and/or interstitial fluid) at or near the pedicle target site may cause shunting as the stimulation signal is applied during the formation, preparation and/or introduction stages of pedicle screw fixation.
The present invention is directed at addressing this need and eliminating, or at least reducing, the effects of the shortcomings of the prior art as described above.